Hypothalamic secretion of thyrotrophin releasing hormone is decreased in male Japanese quail exposed to long daily photoperiods.
Adult male Japanese quail held under short daily photoperiods (8 h light: 16 h darkness; 8L: 16D) had significantly higher plasma concentrations of thyroid-stimulating hormone (TSH), tri-iodothyronine (T3) and thyroxine (T4) than did those kept under long days (16L:8D). When given a single s.c. injection of 50 microgram thyrotrophin releasing hormone (TRH) the birds held under both the 8L: 16D and 16L: 8D photoperiods showed rapid increases in their blood concentrations of TSH, T4 and T3, the amplitude of the TSH response of the birds exposed to 16L: 8D being particularly marked. These results suggest that, in the male quail, long daily photoperiods produce a hypothyroid state as a result of diminished TRH secretion. The synthetic and secretory capacities of the thyroid gland and pituitary thyrotrophs are apparently unimpaired by long days.
D000818:Animals; D003370:Coturnix; D007031:Hypothalamus / Q000378:metabolism*; D008027:Light; D008297:Male; D010507:Periodicity; D013972:Thyrotropin / Q000097:blood; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D014284:Triiodothyronine; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; D013974:Thyroxine